A steering device generally includes a manipulation device, a gear device, a link device, and the like. In this instance, the gear device changes a motion direction of the manipulation device and transfers the changed motion direction to the link device. The link device includes a knuckle assembly in which a tie rod and a ball joint are combined with each other, as a portion of transferring an operation of the gear device to front wheels, and also supporting a relational location of the left and right wheels.
As illustrated in FIG. 1, the knuckle assembly, in which the tie rod and the ball joint are combined with each other, includes a knuckle 100, a ball joint 140, and the tie rod (not illustrated). In this instance, a pair of caliper mounting portions 106a and 106b are integrally formed with the knuckle 100 to mount a caliper (not illustrated). Also, a pair of downwardly protruding ball joint mounting portions 104a and 104b are integrally formed with the knuckle 100 in a lower portion thereof.
As shown in a partial section surface 105, the ball joint mounting portion 104a, which is integrally formed with the knuckle 100 in the lower portion of the knuckle 100, includes a screw groove 109. In this instance, the partial section surface 105 is to indicate the screw groove 109 formed in the ball joint mounting portion 104a. Also, the screw groove 109 is also formed in the ball joint mounting portion 104b which becomes a pair with the ball joint mounting portion 104a. 
As described above, the ball joint 140 is mounted to the ball joint mounting portions 104a and 104b, which are formed with the screw screws 109 respectively, by using bolts 142a and 142b. Hereinafter, a method of mounting the ball joint 140 to the pair of ball joint mounting portions 104a and 104b will be described with reference to FIG. 2.
As illustrated in FIG. 2, the ball joint 140 includes a housing 141, a seat 145, a ball stud 146, a bearing 147, and a dust cover 148. A single finished product, i.e. the ball joint 140 is assembled by assembling each of elements. When the assembly of the ball joint 140 is completed, holes 144a and 144b, which are formed in the housing 141 are matched with the screw grooves 109, and then the ball joint 140 is fixably assembled to the pair of ball joint mounting portions 104a and 104b by using the bolts 142a and 142b. 
Like the conventional art, when a ball joint, which is manufactured as a finished product, is installed to a knuckle by a pressurization method, the ball joint is assembled to the knuckle in a state where the ball joint is assembled as a single finished product. Thus, manufacturing costs for assembling the ball joint and the knuckle may be increased. Also, since a space for combining a bolt or giving a pressure to a housing is required in the knuckle, the size of the knuckle becomes large. Thus, the weight of the knuckle assembled with the ball joint also increases.
In addition, when the ball joint is assembled to the knuckle by the conventional combination method, the ball joint may not be partially exchanged for a simple functional problem of the ball joint. Specifically, since the entire ball joint is required to be exchanged, after service (A/S) costs may be required.